DESCRIPTION

The strtol() function converts the string in nptr to a long value. The
strtoll() function converts the string in nptr to a long long value. The
strtoq() function is a deprecated equivalent of strtoll() and is provided
for backwards compatibility with legacy programs. The conversion is done
according to the given base, which must be a number between 2 and 36 in-
clusive or the special value 0.
The string may begin with an arbitrary amount of whitespace (as deter-
mined by isspace(3)) followed by a single optional '+' or '-' sign. If
base is zero or 16, the string may then include a '0x' prefix, and the
number will be read in base 16; otherwise, a zero base is taken as 10
(decimal) unless the next character is '0', in which case it is taken as
8 (octal).
The remainder of the string is converted to a long value in the obvious
manner, stopping at the first character which is not a valid digit in the
given base. (In bases above 10, the letter 'A' in either upper or lower
case represents 10, 'B' represents 11, and so forth, with 'Z' represent-
ing 35.)
If endptr is non-null, strtol() stores the address of the first invalid
character in *endptr. If there were no digits at all, however, strtol()
stores the original value of nptr in *endptr. (Thus, if *nptr is not '\0'
but **endptr is '\0' on return, the entire string was valid.)

RETURN VALUES

The strtol() function returns the result of the conversion, unless the
value would underflow or overflow. If an underflow occurs, strtol() re-
turns LONG_MIN. If an overflow occurs, strtol() returns LONG_MAX. In both
cases, errno is set to ERANGE.
The strtoll() function has identical return values except that LLONG_MIN
and LLONG_MAX are used to indicate underflow and overflow respectively.

EXAMPLES

Ensuring that a string is a valid number (i.e., in range and containing
no trailing characters) requires clearing errno beforehand explicitly
since errno is not changed on a successful call to strtol(), and the re-
turn value of strtol() cannot be used unambiguously to signal an error:
char *ep;
long lval;
...
errno = 0;
lval = strtol(buf, &ep, 10);
if (buf[0] == '\0' || *ep != '\0')
goto not_a_number;
if (errno == ERANGE && (lval == LONG_MAX || lval == LONG_MIN))
goto out_of_range;
This example will accept "12" but not "12foo" or "12\n". If trailing whi-
tespace is acceptable, further checks must be done on *ep; alternately,
use sscanf(3).
If strtol() is being used instead of atoi(3), error checking is further
complicated because the desired return value is an int rather than a
long; however, on some architectures integers and long integers are the
same size. Thus the following is necessary:
char *ep;
int ival;
long lval;
...
errno = 0;
lval = strtol(buf, &ep, 10);
if (buf[0] == '\0' || *ep != '\0')
goto not_a_number;
if ((errno == ERANGE && (lval == LONG_MAX || lval == LONG_MIN)) ||
(lval > INT_MAX || lval < INT_MIN))
goto out_of_range;
ival = lval;

ERRORS

[ERANGE] The given string was out of range; the value converted has
been clamped.